hiring help

I was at a garden center the other day (where else would I be this time of year?). There was a crew of men painting a barn. I told them when they were done they could paint my house. I need my house painted but at the time I was only kidding. The foreman jumped off the ladder and gave me his business card. It seemed official enough.....

Dh is concerned because many of the painters didn't appear to speak english. What kind of documentation should I require before I allow someone to work on my house? Business licence and proof of workman comp come to mind but is there anything else I should be concerned with?

I have a two story stucco and siding house.......how much do you think it would cost ?- I am concerned that in my lack of experience in these matters that I will pay too much........

Also how do I estimate how much paint a painting contractor might need?

Any help would be appreciated - thanks